Various ambulatory medical devices have been proposed and a number of such devices are commercially available. These devices include, for example, implantable infusion pumps, externally carried infusion pumps, implantable pacemakers, implantable defibrillators, implantable neural stimulators, implantable physiological sensors, externally carried physiologic sensors, and the like.
Numerous electronic devices exist that communicate with one another using electromagnetic radiation of various wavelengths and of various formats. These electronic devices can act as sources of interference that can negatively impact other devices that also need to communicate via telemetry. This is particularly true when other devices attempt to communicate using small signal strengths that are typically associated with the limited power that is available to ambulatory medical devices and most particular to ambulatory devices that are implanted within the body of a patient.
As appropriate operation of medical devices may be critical to those patients being treated using those devices, and as telemetry communications between medical devices and external controllers can greatly enhance the convenience of using such devices, or even be an enabling necessity to the use of such devices (e.g. implantable devices with sophisticated functionality), the operation of such medical devices can benefit significantly by use of telemetry systems and protocols that have features/elements that lead to optimization of various attributes. Attributes of interest may vary with circumstance but some attributes of general interest include (1) flexibility in communicating the wide variety signals that may be useful to controlling and retrieving information from a sophisticated medical device, (2) robustness in distinguishing actual signals from noise, (3) robustness in distinguishing valid signals from corrupt signals, (4) robustness in ascertaining when appropriate communication has occurred and when additional communication must be attempted, (5) a reasonable efficiency in communication time, and/or (6) a reasonable efficiency in electrical power consumption associated with conveying information over the telemetry system.
For example, implantable infusion pumps are generally configured to accept infusion commands from an external communication device via an RF telemetry system, or the like. These commands may be used, inter alia, to set program variables that are in turn used in defining the quantity and/or timing that is used in supplying a drug to the patient. As the dispensing of appropriate amounts of the drug may be critical to the patient's well being, it is desirable that a reliable and trustworthy communication channel exist between the external communication device and the implantable device so that messages from the external communication device requesting drug delivery are received with integrity, confirmation of accurate reception acknowledged in a rapid manner, and minimal electric power consumption occurring in the entire process of listening for a message, receiving the message, and transmitting a response to the message that is appropriately received by the external communication device.
Implantable medical devices typically operate by battery power. The batteries may or may not be rechargeable. Higher consumption of power from an implantable medical device containing non-rechargeable batteries leads to a shortening of the usable life of the device and an associated increased frequency of surgery, potential pain, recovery, and inconvenience. Higher consumption of power from an implantable medical device containing rechargeable batteries leads to more frequent charging periods for the batteries and associated inconvenience and may lead to an overall shortening of the usable life of the device. As such, whether or not an implantable medical device contains rechargeable batteries or non-rechargeable batteries, it is desirable to lower the power consumption of the device. As telemetry reception and transmission are highly energy consumptive, it is desirable to minimize the operation time of telemetry reception and transmission modules. As such it is desirable to ensure that message length is kept to a minimum and that repeated transmissions and attempted receptions of previously sent but unsuccessfully received messages be kept to a minimum.
A need exists in the field for improved telemetry features/elements that tend to optimize each of the above noted attributes individually, with out consideration of the impact on other attributes, or tend to simultaneously optimize groups of selected attributes, or tend to provide a balance between various ones of the attributes.